1. Field of the Invention
The invention relates to a method for fabricating semiconductor device, and more particularly to a method of fabricating flash memory.
2. Description of the Prior Art
A flash memory is a non-volatile memory, which can preserve data within the memory even when an external power supply is off. Recently, because flash memories are electrically re-writable and electrically re-erasable, they have been widely applied in the fabrication of electrical products, such as mobile phones, digital cameras, video players, personal digital assistants (PDA) or systems on a chip (SOC).
To meet the requirements of low power consumption, fast response, low cost and high integration rate of electronic products, integrating processes of different semiconductor devices having various electrical performances and functions is the trend of current semiconductor processes. For example, flash memory cells in the flash memory array area and metal-oxide-semiconductor transistors (MOS) in the logic circuit area may be fabricated in the same chip.
Nevertheless, current approach for integrating flash memory cells and MOS transistors typically encounter serious issues when an oxide cap layer is sandwiched between two polysilicon layers before the polysilicon layers are patterned into word line and gate patterns for the MOS transistors. For instance, the presence of the oxide cap layer often induces defects between control gates of the flash memory cell and lowers the uniformity of the device within wafer. Hence, how to improve the current process flow for integrating flash memory cells and MOS transistors for providing a device with improved performance has become an important task in this field.